Engine Chugging and Vibrations

[Big Orange 78]

78 Chevy K20 w/454 and edelbrock 650 cfm carb w/ th350 tranny. Chuggs when i press on the accelerator around the 25 mph - 45 mph range. Especially noticable when going up hill or when the engine is under a heavy load. Rebuilt the carb and changed the fuel filter to get rid of a flooding problem, however chugging still remains. Still does it and it is more noticable now then before. I am thinking it is a ignition issue. Also I get a vibration when i step on the gas from it seems the front of the truck. Vibration goes away at higher speeds i.e. 65 or higher. But it returns when it get back down around 40-55 mph.I am thinking it is a tire or maybe my drive shaft. does it in 2nd gear as well. Any help is much appreciated!